1. Field of the Invention
This invention generally relates to a semiconductor light emitting element and a semiconductor light emitting device.
2. Related Background Art
Semiconductor light emitting elements are elements that make use of luminescent recombination of electrons and holes injected into pn junctions to emit light from their active layers. They are remarked as inexpensive, long-lifetime light emitting elements.
An issue with such semiconductor light emitting elements is enhancement of light output by enhancing the internal emission efficiency and the light extraction efficiency. Semiconductors in general have higher refractive indices than air. Therefore, only a part of light output inside a semiconductor light emitting element can be extracts externally, and the remainder is reflected back at the interface between the semiconductor light emitting element and air. Therefore, enhancement of the light extraction efficiency is one of issues of semiconductor light emitting elements.
FIG. 20 shows an existing light emitting element disclosed in Japanese Patent Laid-Open Publication No. hei 3-35568. The element includes a bonding substrate 31 transparent to its own emission wavelength, light emitting diode layer 32 and silica layer 33 that are sandwiched between ohmic electrodes 34, 35. A method usable for manufacturing such a semiconductor light emitting element is briefly explained below.
In the first step, the light emitting diode layer 32 is grown on an opaque substrate not shown. Then a bondage substrate 31 transparent to the wavelength of light emitted in the light emitting diode layer 32 is bonded to the light emitting diode layer 32 on the substrate. After that, the opaque substrate, not shown, is removed to obtain an intermediate semiconductor light emitting element. In the next step, the silica layer 33 for concentrating the current to a central part of the light emitting diode layer 32 is formed on the light emitting diode layer 32 as shown in FIG. 20. Thereafter, one of the electricity-conducting ohmic electrodes is formed on the transparent substrate 31, and the other electricity-conducting ohmic electrode 35 is formed over the light emitting diode layer 32 and the silica layer 33, as shown in FIG. 20. After that, through dicing and/or other steps, the semiconductor light emitting element is finally configured quasi hemispherical as shown in FIG. 20.
The semiconductor light emitting element shown in FIG. 20 enhances the light extraction efficiency to some extent by configuring quasi hemispherical.
However, the semiconductor light emitting element shown in FIG. 20 suffers partial blockage of light emitted in the light emitting diode layer 32 by the opaque ohmic electrode 34. Therefore, it could not be sufficiently enhanced in light extraction efficiency.
FIG. 21 shows another existing semiconductor light emitting element disclosed in Japanese Patent Laid-Open Publication No. hei 4-96381. The element includes an AlGaAs thick-film substrate 37, p-type AlGaAs clad layer 38, AlGaAs active layer 39, and n-type AlGaAs clad layer 40 as shown in FIG. 21. This semiconductor light emitting element further includes a semiconductor multi-layered reflective film 41, cap layer 42, Zn-diffused portions 43, p-side electrode 44, and n-side electrode 45. For the purpose of efficiently extracting light emitted in the AlGaAs active layer 39, the semiconductor light emitting element is configured to induce emission of light in a central part of the hemispherical dome.
The semiconductor light emitting element shown in FIG. 21 uses the substrate 37 that is transparent and hemispherical, and locates the opaque electrodes 44, 45 on the surface opposite from the light-extracting surface. Therefore, the semiconductor light emitting element of FIG. 21 is higher in light extraction efficiency than the element of FIG. 20.
However, the element of the type shown in FIG. 21 involves the problem that the production yield or productivity is inevitably low because of extreme difficulty of its mounting. In greater detail, for manufacturing the semiconductor light emitting element of FIG. 21, grooves must be made for isolating the p-side electrode 44 from the n-side electrode 45, and a manufacturing process of Zn-diffused portions 43 is indispensable. These factors made the manufacturing process of the element of FIG. 21 very difficult. Additionally, since the p-side electrode 44 and the n-side electrode 45 are closely located, these electrodes 44, 45 are liable to be short-circuited by a spread of an electrically conductive mounting material during or after the mounting of the element. Furthermore, since those two electrodes 44, 45 need simultaneous positioning, severe preciseness is required for positioning the electrode on the part of the reflector (mounting stem) and the electrodes 44, 45 of the element. These factors inevitably worsened the production yield and the productivity. Furthermore, in the semiconductor light emitting element shown in FIG. 1, a current is injected abeam to the light emitting portion in the central portion of the dome, and this caused uneven emission of light.
As explained above, it has been impossible heretofore to obtain a semiconductor light emitting element high in light extraction efficiency, uniform in emission of light and high in production yield and productivity.
According to embodiments of the present invention, there is provide a semiconductor light emitting element comprising:
a transparent first conduction type substrate having a first surface and a second surface opposed to each other and being transparent to light of a wavelength xcex;
a semiconductor epitaxial layer formed on a location of the first surface of the substrate directly or via a buffer layer, and including a semiconductor layer of a first conduction type formed in electrical connection with the substrate, an active layer formed on the semiconductor layer of the first conduction type to emit light of the wavelength xcex and a semiconductor layer of a second conduction type formed on the active layer;
a first electrode formed in electrical connection with the semiconductor layer of the second conduction type of the semiconductor epitaxial layer on a location of a surface of the semiconductor epitaxial layer opposite from the substrate;
a second electrode formed in electrical connection with the substrate on a location of the second surface of the substrate offset from alignment with the first electrode; and
a groove formed to indent from the second surface of the substrate toward the first surface thereof in a location between the first electrode and the second electrode.
According to embodiments of the present invention, there is provide a semiconductor light emitting device comprising:
a semiconductor light emitting element having:
a transparent first conduction type substrate having a first surface and a second surface opposed to each other and being transparent to light of a wavelength xcex;
a semiconductor epitaxial layer formed on a location of the first surface of the substrate directly or via a buffer layer, and including a semiconductor layer of a first conduction type formed in electrical connection with the substrate, an active layer formed on the semiconductor layer of the first conduction type to emit light of the wavelength xcex and a semiconductor layer of a second conduction type formed on the active layer;
a first electrode formed in electrical connection with the semiconductor layer of the second conduction type of the semiconductor epitaxial layer on a location of a surface of the semiconductor epitaxial layer opposite from the substrate;
a second electrode formed in electrical connection with the substrate on a location of the second surface of the substrate offset from alignment with the first electrode; and
a groove formed to indent from the second surface of the substrate toward the first surface thereof in a location between the first electrode and the second electrode;
a reflector; and
an electrically conductive mounting material for mounting the first electrode of the semiconductor light emitting element on the reflector.
According to embodiments of the present invention, there is further provide a semiconductor light emitting device comprising:
a semiconductor light emitting element having:
a GaP substrate of a first conduction type, having a first surface and a second surface opposed to each other and being translucent to light of a wavelength xcex;
a semiconductor epitaxial layer formed on a location of the first surface of the substrate via a buffer layer of a GaP compound semiconductor, and including a semiconductor layer of a first conduction type formed in electrical connection with the GaP substrate, an active layer formed on the semiconductor layer of the first conduction type to emit light of the wavelength xcex, a semiconductor layer of a second conduction type formed on the active layer, a reflective layer of the second conduction type formed on the semiconductor layer of the second conduction type to reflect light of the wavelength xcex, and a contact layer of the second conduction type formed on the reflective layer, the semiconductor layer of the first conduction type, the active layer and the semiconductor layer of the second conduction type being made of InGaAlP compound semiconductor and being different in lattice constant and material from the GaP substrate, the contact layer of the second conduction type being made of a GaAs compound semiconductor;
a first electrode formed on a location of the contact layer of the second conduction type in electrical connection therewith;
a second electrode formed on a location of the second surface of the substrate in electrical connection therewith; and
a wedge-shaped groove formed to indent from the second surface of the substrate toward the first surface thereof in a location between the first electrode and the second electrode, and having a pass-through surface portion permitting the light from the active layer to pass through externally of the substrate and a reflective surface portion for reflecting light passing through the pass-through surface potion;
a reflector; and
an electrically conductive mounting material for mounting the first electrode of the semiconductor light emitting element on the reflector.